The invention relates generally to a retention pin for a gas turbine nozzle and more specifically to a fully contained retention pin for an outer sidewall retention scheme for a nozzle.
In a gas turbine, hot gases of combustion flow from combustors through first-stage nozzles and buckets and through the nozzles and buckets of follow-on turbine stages. The first-stage nozzles typically include an annular array or assemblage of cast nozzle segments each containing one or more nozzle stator vanes per segment. Each first-stage nozzle segment also includes inner and outer sidewall portions spaced radially from one another. Upon assembly of the nozzle segments, the stator vanes are circumferentially spaced from one another to form an annular array thereof between annular inner and outer sidewalls. A nozzle retaining ring coupled to the outer sidewall of the first-stage nozzles supports the first-stage nozzles in the gas flow path of the turbine. An annular nozzle support ring, preferably split at a horizontal midline, is engaged by the inner sidewall and may support the first-stage nozzles against axial movement.
Side seals may seal the annular array of segments one to the other along adjoining circumferential edges. The side seals seal between a high pressure region radially inwardly of the inner sidewall and radially outward of the outer sidewall, i.e., compressor discharge air at high pressure, and the hot gases of combustion in the hot gas flow path which are at a lower pressure. Chordal hinge seals are used to seal between the inner sidewall of the first-stage nozzles and an axially facing surface of the nozzle support ring and between the outer sidewall and a shroud for the first stage bucket.
FIG. 1 illustrates a prior art sidewall retention system 100 for a first stage nozzle 110. The first stage nozzle 110 includes an outer sidewall 115, an inner sidewall 120 and an airfoil 125 positioned between a nozzle retaining ring 130 and a nozzle support ring 135. The nozzle retaining ring 130 and the support ring 135 are attached to the casing of the turbine (not shown). The first stage nozzle also includes chordal hinge rails for the inner sidewall and outer sidewall. The chordal hinge rail 145 on the inner sidewall 120 provides axial support for the nozzle 110 against the support ring 135 and the chordal hinge rail 150 provides axial support for the nozzle 110 against the shroud 160 of the first stage bucket 170. The inner chordal hinge rail 145 and outer chordal hinge rail 150 further provide chordal hinge seals 147, 152.
The chordal hinge rail 150 on the outer sidewall 115 of the nozzle 110 projects outward radially from the outer sidewall 115. The chordal hinge rail 150 incorporates a forward-facing annular retaining land 175 at its outermost radial projection. The retaining land 175 mates with an aft-facing annular groove 180 established by an aft-facing retaining hook 185 on the retaining ring. The retaining land 175 of the chordal hinge rail 150 acting on the retaining hook 185 of the retaining ring 130 provides radial support for the nozzle 110. The annular retaining hook 185 may be divided into segments (not shown). Circumferential support is provided by an anti-rotation pin (not shown) that passes through the retaining ring 130 and the retaining land 175.
Power generation gas turbines traditionally use some type of hook retention scheme. Improvements have been made on the traditional hook retention scheme by changing from a continuous hook arrangement, typical in FA class machines by the General Electric Company to a segmented hook arrangement, typical in FB class machines by General Electric Company. This change resulted in more determinate nozzle loading and better nozzle sealing but also resulted in poor thermal isolation of the retaining ring and thereby a substantial cost increase to the nozzle arrangement. Some of the field issues related to hook retention designs include poor chordal hinge sealing, retaining ring out of roundness, and high trailing edge stresses.
Accordingly, there is a need to provide determinate nozzle loading and improved sealing while also improving thermal isolation of the retaining ring, reducing cost, and improving assembly flexibility of the nozzle arrangement.